Here are my simple points why universal PCB can't work.
1) different power density. Just compare KnC or Spondoolies chips with BF, Bitmain or others. Two different ways of power density. SFARDS just in the middle. Different power density needs different PCB design and different heatsink design.
3) total output power. It is based on power density. We can see extremely increasing power density with the same case size in Bitmain's products beginning from Antminer S1 to Antminer S7 or S9. One single heatsink can't handle 700W on multiple chips. Even 300W is too much as we seen on S5 failure rate.
I dont think manufacturers will standardize a design anytime soon - by offering a full product their margins are probably improved
as for power density/draw, a universal heatsink isnt ideal but it is pretty sufficient. simply upgrading the fan/fanspeed could allow a +/- 50% power capacity.
The bigger issue is board layout, where all components were set to a specific maximum thickness in heatsinked areas (so that only critical parts (ASIC, regulators) are snug to heatsink and other components are not), and this could prove inconvenient to some layouts